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Abstract:

A method for calculating the geographical position of a user equipment
(UE) unit includes collecting position parameters conveying the relative
position of the UE unit from two or more base stations using technologies
mandated for the modern wireless networks. Particularly, know
(predetermined) signals embedded in the downlink and uplink subframes,
such as preambles, pilots, ranging codes are used for determining the
coordinates of the UE unit. In addition, the methods and systems proposed
here take advantage of the multiple antennas systems mandated at both the
UE and BTS.

Claims:

1. A method for determining the location of a user equipment (UE) unit
operating within the coverage area of a plurality of antennae of a base
transceiver station (BTS) in a radio access network, said UE unit
transmitting uplink a specified periodic bit sequence, comprising: i) at
said BTS, monitoring the incoming traffic received from said UE unit over
two receive antennae for detecting said specified periodic bit sequence;
ii) measuring a respective first and second position parameter from said
specified periodic bit sequence received as said first and second
antenna, respectively; and iii) processing said first and second position
parameters at said BTS for establishing the geographical coordinates of
said UE unit.

2. A method as claimed in claim 1, wherein said UE unit is triggered to
transmit a signal known to BTS as said specified periodic bit sequence.

3. A method as claimed in claim 1, wherein said first and second position
parameters are a first and a second time of arrival (TOA).

4. A method as claimed in claim 3, wherein step iii) comprises:
generating a first and a second function, representing a first and a
second circle having said first and respectively second TOA as a radius
and said first and second antenna as a center; and establishing the
geographical coordinates of said UE unit at the intersection between said
two circles.

5. A method as claimed in claim 1, wherein said first position parameter
is the angle or arrival (AOA) of said specified periodic bit sequence on
said first antenna, and the second position parameter is the distance
between said UE unit and said second antennae.

6. A method as claimed in claim 5, wherein step iii) comprises
calculating the coordinates of said UE unit relative to said BTS and
establishing the geographical coordinates of said UE unit based on the
coordinates of said UE unit relative to said BTS.

7. A method as claimed in claim 1, wherein said radio access network is
one of a WiMax, a 3GPP LTE and a UMB network.

8. A method as claimed in claim 1, wherein said specified periodic bit
sequence is a ranging code transmitted in the uplink subframes by said UE
unit.

9. A method as claimed in claim 1, further comprising operating said UE
unit in a location ranging mode, where said specified periodic bit
sequence is a location ranging code transmitted by said UE unit.

10. A method as claimed in claim 9, wherein said location ranging code
includes a ranging code known to said BTS and a caller identification.

11. A location identification module for a base transceiver station BTS
operating in a radio access network, said BTS having a first and a second
antennae, comprising: a first monitoring unit for monitoring the incoming
traffic received on the first antenna and identifying said specified
periodic bit sequence received from a user equipment (UE) unit positioned
in the area of coverage of said BTS and determining a first position
parameter; a second monitoring unit for monitoring the incoming traffic
received on the second antenna and identifying said specified periodic
bit sequence received from said UE unit and determining a second position
parameter; and a coordinate estimator for processing said two position
parameters and establishing the geographical coordinates of said UE unit.

12. A location identification module as claimed in claim 11, wherein said
radio access network is a WiMax network.

13. A location identification module as claimed in claim 12, wherein said
specified periodic bit sequence is a ranging code transmitted in the
uplink subframes by said UE unit.

14. A location identification module as claimed in claim 11, wherein said
first and second position parameters are a first and a second time of
arrival (TOA) of said specified periodic bit sequence at said first and
second antenna.

15. A location identification module as claimed in claim 11 wherein said
first position parameter is the angle or arrival (AOA) of said specified
periodic bit sequence on said first antenna, and the second position
parameter is the distance between said UE unit and said second antennae
measured at said BTS.

16. A location identification module as claimed in claim 11, further
comprising a transceiver for receiving two additional position parameters
from two neighbouring BTSs and transmitting said first position parameter
to said two neighbouring BTSs, wherein said two additional position
parameters are processed with said first position parameter for
establishing the geographical coordinates of said UE unit.

17. A method as claimed in claim 1, wherein said specified periodic bit
sequence is an additional symbol transmitted in said uplink frame, which
includes an identification of said UE unit and a request for identifying
the geographical coordinates of said UE unit.

Description:

FIELD OF THE INVENTION

[0001] The invention is directed to mobile radio access systems and in
particular to systems and methods for determining the geographical
location of a caller operating a mobile (wireless) device over a mobile
radio access system.

BACKGROUND

[0002] Wireless networks have significantly impacted the world in the last
debacles and their uses continue to grow significantly. People and
businesses use wireless networks to send and share data quickly whether
it be in a small office building or across the world. Emergency services
such as the police department utilize wireless networks to communicate
important information quickly. Another important use for wireless
networks is as an inexpensive and rapid way for connection to the
Internet in countries and regions where the telecom infrastructure is
poor or there is a lack of resources, like in many developing countries.
One of the latest such wireless technologies is WiMax (Worldwide
Interoperability for Microwave Access).

[0003] A brief review of the WiMax technology follows for providing the
readers with a better understanding of the invention. It is to be noted
that the invention is not limited to the WiMax technology, but it is
applicable to any wireless technology that uses predetermined periodic
bit sequences and multiple antennas in downlink and uplink frames, such
as frame preambles, pilot tones, and/or ranging codes used by WiMax.

[0004] WiMax is an emerging telecommunications technology that provides
long range wireless communication, and enables both point-to-point and
full mobile cellular type access. This technology is based on IEEE 802.16
standard. The initial draft standard for this technology, called 802.16d,
or 802.16-2004 has never reached the standard status. Systems built using
802.16-2004 (802.16d) and OFDM PHY with 256 carriers as the air
interface, are generally referred to as "fixed WiMax".

[0005] The next version of the draft, 802.16e (or 802.16-2005), which is
an amendment to 802.16d, is often referred to as "mobile WiMax". This
term refers to wireless systems that use 802.16e-2005 and OFDMA
(orthogonal frequency-division multiple access) with 128, 512, 1024 and
2048 carriers as the air interface. In OFDMA, a spread-coded string of
symbols of a signal to be transmitted is modulated on subcarriers which
are preferably distributed into a broad frequency band. OFDMA assigns
subsets of subcarriers to individual users, and based on feedback about
the channel conditions, the system can implement adaptive
user-to-subcarrier assignment.

[0006] Mobile WiMax implementations can be used to deliver both fixed and
mobile services. The mobile WiMax also uses Multiple Antenna Support
through Multiple-Input Multiple-Output communications (MIMO). A base
transceiver station (BTS), also called a base station (BT), uses at least
two receiving antennae and two transmitting antennae and the user
equipment (UE unit) uses at least two receiving antennae and a
transmitting antenna. This brings potential benefits in terms of
coverage, spatial diversity and spatial multiplexing, interference
cancelation, frequency re-use and spectrum efficiency.

[0007] Mobile WiMax has just been approved by ITU, and telecommunication
companies such as Sprint-Nextel in USA and France Telecom in France have
announced their intention to deploy such systems. In Canada, Rogers
communications and Bell Canada started to provide WiMax based Broadband
Internet service on 2.5 GHz frequency band, covering most major cities
like Toronto using Motorola's DRM units.

[0008] In the meantime, the advancements in the wireless networks
technologies enabled deployment of wireless location positioning systems,
particularly systems designed to locate the geographical position of
callers that place emergency calls (such as "911" in SUA and Canada)
using a mobile device. One of the purposes of this service is to enable a
wireless network to identify to which Public Safety Answering Point
(PSAP) to route an emergency call and to inform the PSAP that answers the
call where the caller is. A PSAP will then exploit the knowledge about
where a caller is located and provide the information of his/her
surroundings such as directions, nearby restaurants, museums, etc to the
emergency services. Location based services have been a hot topic for B3G
(beyond 3G) wireless systems such as 3GPP/UMTS/LTE (long term evolution),
WiMax/IEEE 802.16e, UMB (ultra mobile broadband) etc.

[0009] Currently, the "911" service is capable of locating fixed phones in
most geographical areas in the United States and Canada; other countries
have similar emergency services. For wireline "911", the location is an
address.

[0010] The U.S. Federal Communications Commission (FCC) rolled out a
location technology called E911 (Enhanced 911), which enables
cellular/mobile devices to process 911 emergency calls for timely
deployment of assistance. For Wireless E911, the location is a
coordinate. The FCC has rolled out E911 in two phases. In 1998, Phase I
required that mobile phone carriers identify the originating caller phone
number and the location of the signal tower, or cell, with an accuracy of
less than one mile. In 2001, Phase II required that each mobile phone
company doing business in the United States must offer either handset or
network-based location detection capability so that the caller's
geographic location, termed ALI (Automatic Location Identification) be
provided with an accuracy of less than 100 meters.

[0011] Several methods are known for determining the location of a mobile
caller (MC) as required by Phase I. These are called "network based"
methods since they employ a wide area array of antennas and transceivers
coupled together, and a mobile caller can be located whenever contained
within the area that is covered by the respective transceivers/antennae.
Such methods usually require minimal modifications in the mobile devices
involved in ALI. However, the current network based methods are not very
accurate and may not work particularly well in an indoor environment.

[0012] Foe example, it is known to measure the Angle of Arrival (AOA) of a
signal received at two (or more) base station antennae; trigonometric
calculations then establish the caller's coordinates using the known
location of the antennae and the AOA of the received signal.

[0013] It is also known to identify the location of a MC by measuring the
Time of Arrival (TOA) of a signal emitted by the caller's mobile at three
(or more) network antennae. The location of the MC can be then determined
knowing the location of these antennae, the three TOA's measurements, and
the velocity of the signal (the velocity of electromagnetic waves/light).
This is accomplished by determining the geometric locus of the points at
a fixed, known distance (range) from a fixed point (the location of the
MC); the range is determined from the TOA. As this method gives two
points, a fourth antenna is used sometimes to remove this ambiguity or to
compensate for clock discrepancies.

[0014] Other network based solutions provide the location of the mobile by
measuring at a base station the round-trip delay of a signal sent from
the base station to mobile and back, or in other words, the time elapsed
between transmission of a signal from the base station and reception of
the response from the mobile. This round trip delay is then used to
evaluate the distance between the two; the distance and the AOA
measurement at the base station are used to estimate the coordinates of
the mobile.

[0015] However, the AOA, TOA and round trip delay methods are based on
line of sight distance measurements (straight distance between the UE
unit and the antennae), which can be difficult or impossible to determine
in mountainous terrain or in the cities around high buildings and other
obstacles. Therefore, the results obtained with these methods are
inaccurate. In addition, the location of the caller is not very accurate,
especially in the case of indoor calls.

[0016] Currently, Phase II of the E911 technology is mainly implemented
using Global Positioning System (GPS) embedded into the caller's
equipment. The GPS units are embedded in the mobile devices and normally
determine their position by computing relative times of arrival of
signals transmitted simultaneously from a multiplicity of GPS satellites
(i.e. GPS/NAVSTAR). These satellites transmit both satellite positioning
data and GPS-assist data; such as clock timing or "ephemeris" data. If
the roaming device is known to be essentially on the ground (e.g.,
mounted in a car), the earth globe, with proper topography, can be used
as an additional reference "sphere" to refine the TOA calculations.

[0017] However, the process of searching for and acquiring GPS signals,
reading the ephemeris data for a multiplicity of satellites and computing
the location of the receiver from this data is time consuming, often
requiring several minutes. In many cases, this lengthy processing time is
unacceptable, particularly in emergency situations where location is
being determined for a 911 dispatch centre. In addition, in order to use
GPS, the mobile device must be GPS-enabled, which is not always the case.
Equipping the mobiles with GPS units also increases the cost, which may
become prohibitive for many. Still further, a GSP receiver does not
operate properly in some types of environment such as indoors or where
satellite signals get blocked.

[0018] All the methods described above have not yet provided satisfactory
solutions to the problem of wirelessly determining the location of
callers using small, inexpensive and low power roaming devices. Also,
current methods and systems do not operate well over a wide area, without
requiring a dedicated infrastructure.

[0019] Therefore, a need to improve location determination still exists,
both with a view to enhance the services offered to mobile device users
and particularly in with of the E911 regulations by the FCC in the US.

SUMMARY OF THE INVENTION

[0020] It is an object of the invention to provide methods and systems for
determining the location of a mobile caller in compliance with FCC
requirements.

[0021] Another object of the invention is to provide methods and systems
for determining the location of a mobile caller that are inexpensive and
applicable over a wide area, without requiring a dedicated
infrastructure.

[0022] Accordingly, the'invention provides method for determining the
location of a user equipment (UE) unit operating within the coverage area
of a two or more base transceiver stations (BTS) that transmit a
specified periodic bit sequence over a radio access network, comprising:
a) at the UE unit, monitoring incoming traffic received from the BTSs for
detecting the specified periodic bit sequence; b) determining from the
specified periodic bit sequences at least two position parameters that
convey the relative position of the UE unit to two or more of the BTSs;
and c) processing the position parameters for establishing the
geographical coordinates of the UE unit.

[0023] The invention also provides a location identification module for a
user equipment (UE) unit equipped with a first and a second antenna,
comprising: a monitoring unit for monitoring the incoming traffic and
identifying a specified periodic bit sequence received from at least two
neighbouring base transceiver stations (BTSs); a position parameters
calculation arrangement for determining from the specified periodic bit
sequences two position parameters conveying the relative position of the
UE unit from the respective BTSs; and a coordinate estimator for
processing the two position parameters and establishing the geographical
coordinates of the UE unit.

[0024] According to another aspect of the invention, there is provided a
method for determining the location of a user equipment (UE) unit
operating within the coverage area of a plurality of antennae of a base
transceiver station (BTS) in a radio access network, the UE unit
transmitting uplink a specified periodic bit sequence. The method
comprises i) at the BTS, monitoring the incoming traffic received from
the UE unit over two receive antennae for detecting the specified
periodic bit sequence; ii) measuring a respective first and second
position parameter from the specified periodic bit sequence received as
the first and second antenna, respectively; and iii) processing the first
and second position parameters at the BTS for establishing the
geographical coordinates of the UE unit.

[0025] Still further, the invention provides a location identification
module for a base transceiver station (BTS) operating in a radio access
network, the BTS having a first and a second antennae, comprising: a
first monitoring unit for monitoring the incoming traffic received on the
first antenna and identifying the specified periodic bit sequence
received from a user equipment (UE) unit positioned in the area of
coverage of the BTS and determining a first position parameter; a second
monitoring unit for monitoring the incoming traffic received on the
second antenna and identifying the specified periodic bit sequence
received from the UE unit and determining a second position parameter;
and a coordinate estimator for processing the two position parameters and
establishing the geographical coordinates of the UE unit.

[0026] Advantageously, the invention does not require to equip a mobile
with GPS for automatic location identification, thus enabling low cost
user equipment to readily locate itself. In addition, since adoption of
the WiMax standard, the trend in the wireless networking is to adopt
similar technologies in the next generations of wireless networks such as
3GPP LTE and UMB systems. As such, the invention can be also applied to
3GPP LTE and UMB systems.

[0027] Another advantage of the method and systems of the invention is
that it allows implementation of E911 location based services within
WiMax systems using WiMax equipment. The invention is a good complement
to, or replacement for GPS in some environments, particularly indoor
environments where supposedly 80% of WiMax and 911 services users are
situated, particularly once small WiMax BT or access points and Femto
BTSs will be installed.

BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The invention is next described with reference to the following
drawings, where like reference numerals designate corresponding parts
throughout the several views.

[0029] FIG. 1A shows an example of a frame for the mobile WiMax system.

[0030] FIG. 1B illustrates an example of the preamble structure for OFDM
modulation in 10 MHz band using 1024-FFT (Fast Fourier Transform).

[0031] FIGS. 2A and 2B show an embodiment of the invention whereby a user
equipment (UE) unit determines its location using the preamble or the
pilot tones inherently present in the WiMax downlink frames.

[0032]FIG. 3 shows another embodiment of the invention where a UE unit
determines its location using the angle of arrival of the preambles or
pilot tones inherently present in WiMax systems.

[0033]FIG. 4 is a block diagram of a user equipment unit according to an
embodiment of the invention.

[0034]FIG. 5 illustrates still another embodiment of the invention where
location of the UE is determined by cooperation between base stations
using the two antennae inherently present in the UE unit.

[0035]FIG. 6 shows an embodiment of the invention where a base station
determines the location of a UE unit using the ranging codes transmitted
by the UE.

[0036]FIG. 7 illustrates how a base station with multiple antennae
identifies the location of a UE unit according to still another
embodiment of the invention.

[0037]FIG. 8 is a block diagram of the base station according to an
embodiment of the invention.

[0038]FIG. 9 illustrates use of an additional symbol in the upstream
subframe for transmitting location requests and UE unit identification
information to the BTS.

DESCRIPTION OF THE EMBODIMENTS OF THE INVENTION

[0039] In this specification, the terms "mobile caller" or "caller" is
used to designate a user who currently accesses the services offered by a
wireless network/services provider. The term "user equipment (UE unit)",
"mobile devices (MD)", or "mobile station (MS)", is used to designate
wireless-enabled devices such as handsets, phones, notebooks, and other
wireless equipment used by subscribers to connect to a wireless or
wireline network for exchange of digital or analog formatted information.

[0040] The term "base station (BS)" or "base transceiver station (BTS)"
refers to the equipment in a wireless access network (WAN) which
facilitates wireless access of mobile devices to a wireless or/and
wireline communication network. The term "access point (AP)" refers to an
indoor access point, which enables connection of indoors UE units to a
wireless or a wireline network. BTSs and APs operate in a similar way
from the point of view of the present invention, so that the term "BTS"
also includes "AP". This specification uses the term "serving BTS" for
the base station that currently connects the UE unit to the access
network. The term "neighbouring BTS" is used for the BTSs in immediate
proximity of the UE unit; a UE unit is in the coverage area of these
neighbouring BTSs. This term includes the serving BTS.

[0041] The recognized meaning of the terms "uplink" and "downlink" is used
throughout this specification. Namely, "uplink" refers to the traffic
direction from a UE to a BTS and "downlink" refers to the traffic from a
BTS to one or more UEs. The term "incoming traffic", which is a relative
tern, refers to the traffic arriving at a certain network entity on an
uplink or a downlink.

[0042] While the invention is particularly relevant to E911 systems, it
can be equally applied for locating a UE unit for other types of existing
or emerging location positioning systems and services. E911 service is
referred to here since this service recently became a mandatory
requirement for WiMax service providers and users, with the advent of
802.16e (mobile WiMax) adoption.

[0043] Also, the invention is not restricted to WiMax systems; it can be
used with other current and emerging wireless technologies that mandate
broadcast of predetermined (specific) periodic bit sequences in the
downlink sub-frames and/or require transmission of specific periodic bit
sequences in the uplink sub-frames, as discussed next. Examples of such
wireless networks are 3GPP LTE and UMB systems.

[0044] FIG. 1A shows an example of a WiMax frame 10, illustrating the
downlink (DL) subframe 11 and uplink (UL) subframe 12. In the direction
from the BTS to the UE unit, shown by the downlink subframe 10, a BTS
sends a preamble 13, which is used by the UE unit for cell/sector
identification, frequency reuse factor, synchronization and channel
performance assessment. The preamble has one of 128 distinct patterns;
each sector in which a BTS transmits is identified in the preamble, using
a cell ID. Thus, the neighbouring cells or sectors have different
patterns so that the UE units are able to distinguish a cell or sector
from others. An initial synchronization operation determines the start of
the frame by observing the autocorrelation of the time domain replica of
the preamble, with a view to detect the preamble. Preambles are usually
sent with a boosted power (say, 2.5 dB higher than the data signal).

[0045] FIG. 1B shows the subcarriers used by mobile WiMax systems for
FTT-1024 variant. In this embodiment, the entire transmission band of
11.2 MHz has been divided into 1024 bins, among which the middle 852 bins
are used to carry the preamble (the DC bin carries "0").

[0046] These 852 bins are further divided into 3 sets for 3 sectors (as
indicated above, a BTS within a sector transmits different preambles from
the BTSs within the other two sectors) by applying the following formula:

PreambleCarrierSetn=n+3k EQ1

[0047] where: PreambleCarrierSetn is the carrier/bin number in
carrier-setn, n is the number of the preamble carrier-set indexed as 0,
1, 2, . . . ; and k is a running index from 0 to 283.

[0052] As seen, each set has 284 carriers and the actual DC carrier number
512 maps to preamble carrier 426 belonging to carrier-set 0. Each
preamble code is predesigned and assigned to a sector when the respective
system (BTS) is deployed. The preamble of a downlink frame is generically
referred to here as a downlink "specified periodic bit sequence", where
the word "specified" is used to indicate that the bit sequence is known
to the receiver, and the word "periodic" is used to indicate that the bit
sequence is transmitted periodically in the downlink (with each downlink
frame).

[0053] FIGS. 2A, 2B and 3 show various automatic location identification
(ALI) methods where the UE identifies the coordinates of its location and
transmits these with the call to a PSAP (Public Safety Answering Point)
or the like. FIGS. 2A and 2B show an embodiment of the invention where
the UE unit determines its coordinates using the preamble received in the
WiMax downlink subframes. Here, an UE unit places a "911" call, or the
like, to its serving BTS from a location UE(x,y), where x and y are the
coordinates (unknown) of the US unit. The UE unit is in proximity of at
least three BTSs, namely the serving BTS, designated with BTS1, and two
neighbouring BTSs designated with BTS2 and BTS3. The coordinates of these
BTSs are known, in many cases they are ascertained using GPS equipment
customary embedded in the BTSs. The position of each BTS is denoted with
BTS1(x1, y1) BTS2(x2,y2) and BTS3(x3,y3), where x1,y1, x2,y2 and x3,y3
are the respective coordinates.

[0054] As indicated above, each BTS transmits periodically a certain bit
sequence in the downlink frame. In this embodiment, this known periodic
bit sequence is the downlink preamble for the respective sector: these
are denoted with Preamble1, Preamble2 and respectively Preamble3. The UE
unit monitors constantly the incoming traffic to identify the preambles.
Since the distances to BS1, BS2 and BS3 are different, the UE unit
receives the preamble from the three BTs at different times; let's denote
these times of arrival with TOA1, TOA2 and TOA3.

[0055] The UE unit aligns the times of arrival of the preambles Preamble2
and Preamble3 received form BTS2 and BTS3 to the time of arrival of the
Preamble1 received from the serving BTS1. In FIG. 2B, the time difference
between the arrival of the Preamble1 and Preamble2 is denoted with T12,
and the time differences between the arrival of the Preamble1 and
Preamble3 is denoted with T13. These time differences are referred to
generically as "position parameters" and they include inherently the
relative position of the UE unit with respect to the BTSs. As the
geographical position of the UE unit is fully determined by two unknowns
(UE coordinates x and y), two such position parameters will suffice to
determine the coordinates x, y.

[0056] In order to determine T12 and T13, UE unit generates local copies
of the Preamble2 and Preamble3, and correlates the data blocks from these
copies with the data block from Preamble1 received from the serving BTS.
The correlation can be performed either in the time domain or in the
frequency domain. Then, the UE unit solves the following equations of two
unknowns (x and y) to obtain its position UE(x,y)

[0058] Once the geographical coordinates (x, y) of the UE unit are
determined, the location data is transmitted to the PSAP or other
relevant services according to the acknowledged scope of location
identification. For example, a 911 call is routed in North America to the
emergency services dispatch. The PSAP further process this information to
establish practical details about the location of the caller, using for
example maps of the respective area, or street addresses, etc.

[0059] Similarly to the preamble, the BTS also transmits pilot signals in
the downlink frames on reference carriers. Different sub-channelization
schemes have different pilot designs in terms of pilot position in the
transmission band and theft number, and the data they carry. The pilots
in each sector are associated with a pseudo-random bit sequence that is
established based on the cell ID. As each pilot in a sector carries the
same predetermined reference symbol, a UE unit can recognize that
sector's pilots by identifying the cell ID from the respective preamble.
Like the preambles, the pilots are also transmitted with a boosted power
(2.5 dB higher than data signal).

[0060] Since the magnitude and phase of the pilot carriers are known to
the receiver, they are used in WiMax systems for time and frequency
synchronization, channel estimation, signal-to-interference/noise ratio
measurement, etc. For the 10 MHz, FFT-1024 variant of the mobile WiMax,
there are 120 pilots inserted every OFDM symbol. These properties of the
pilots are used in this invention for determining the geographical
coordinates of a mobile device, as discussed above in connection with
FIGS. 2A and 2B for the preamble.

[0061] The present invention also proposes to use the WiMax downlink
pilots for measuring the position parameters T12 and T13; the pilots are
also generically referred to as a downlink "specified periodic bit
sequence". In this case, T12 and T13 provide the time differences between
the time of arrival of the pilots received from the neighboring base
stations BTS2, BTS3 and the time of arrival of the pilot received from
the serving base station BTS1.

[0062] It is to be noted that the invention is not limited to establishing
the UE unit coordinates using one of the preamble and pilots embodiments
described above. Rather, the UE unit may use both the preamble and the
pilot methods. In addition, a UE unit may use any other bit sequence of a
known pattern that is transmitted periodically in the downlink frame of
other wireless communication technologies (current or emerging) for
determining its position.

[0063] As also indicated above, the mobile WiMax Standard mandates that
the mobile be equipped with minimum two antennae separated by a distance
of a half wavelength. In the embodiment of FIG. 3, the UE unit determines
its location using the downlink specified periodic bit sequence (the
preamble, the pilots, or both) inherently broadcast by the BTSs in WiMax
systems (and may be other emerging wireless systems). As in the previous
example, the UE unit continuously monitors the downlink transmissions
received from neighbouring base stations. Each antenna A1, A2 receives
the signals from the BTS1, BTS2 and BTS3 at a different angle of arrival
(AOA). The UE unit selects the strongest two signals it receives at these
two antennae; let's assume that these are the pilot or preamble received
from the serving station BTS1 located at BTS1(x1,y1) and from base
station BTS2, located at BTS2(x2,y2). The UE unit then estimates the
angles of arrival AOA1 and AOA2 of these two signals, and determines
coordinates x and y by solving a linear equations of two unknowns:

[0064] As before, the coordinates are used to establish the detailed
location information using maps or any other type of known location data.
For example, if the UE unit is equipped with a GPS, the particulars of
location (x, y) may be detailed by the UE unit and transmitted
automatically to the 911 operator (or any other relevant party). Such
details may include a street address, including direction for the rescue
team, or details about the indoor location of a caller, such as the
building, floor, etc. The information may also include explanations as to
the geographical coordinates if the caller is not in an inhabited area,
or directions to any relevant landmarks for assisting the rescuers to
locate the position fast. It is to be noted that this embodiment is
recommendable for determining the location of indoor callers.

[0065]FIG. 4 shows a block diagram of the UE unit showing generically an
access network interface 41 that connects the UE unit to the wireless
access network, a transceiver 45 for data communication and processing
and a user interface 48 that enables the user to operate the UE unit. In
very broad terms, for the downlink direction of traffic (BTS to UE),
interface 41 is responsible with processing the downlink frames received
from the BTSs over Antenna1 and/or Antenna2. The receive side of
transceiver 45 extracts the data from the downlink subframe and processes
it, and the transmitter side of transceiver 45 provides the processed
data to the user over user interface 48.

[0066]FIG. 4 shows a location identification module 40 which includes the
units relevant to an embodiment of this invention. A monitoring unit 42
monitors the incoming traffic, detects the specified periodic bit
sequence (preamble or pilot) and identifies the BTS that transmitted it.
A position parameters calculation arrangement 43 determines from the bit
sequence received from the BTSs two position parameters that inherently
convey the relative position of the UE unit with respect to two or more
BTSs. For example, and as discussed above, the position parameters may be
T12 and T13 for the embodiment shown in FIG. 2A or/and the angle of
arrival AOA1 and AOA2 for the embodiment of FIG. 3. The position
parameters are then provided to a coordinates estimator 44.

[0067] For the TOA embodiment (FIG. 2A), copies of the respective bit
sequences are temporarily stored in a memory 49, for enabling the
coordinate estimator unit 44 to correlate the copies of the sequences
with the sequence received from the serving BTS for determining T12 and
T13; coordinates estimator 44 then determines the coordinates of the UE
unit, based on the time differences 112 and T13 using EQ2. Alternatively,
if the monitoring unit provides the angle of arrival, coordinate
estimator 44 determines the coordinates of the UE unit using EQ3.

[0068]FIG. 4 also shows a stand-alone memory 49 which is a general
purpose memory for enabling operation of the coordinates estimator. For
example, memory 49 may be used for temporarily storing the coordinates of
the serving base station and of the neighbouring BTSs for enabling the UE
unit to calculate the UE unit coordinates based on the known coordinates
of the BTSs. The geographical position of the BTSs may also be stored
temporarily in memory 49, if transmitted to the UE unit through messaging
once the UE unit initiates the respective call. Alternatively, the memory
49 may keep a list of the BTSs present in the respective access network
once it enters into the area served by that network. Other ways of
obtaining the coordinates of the BTS are possible, but these are beyond
the scope of the present invention. It is also to be mentioned that
memory 49 may be implemented in any other memory already present at the
UE unit.

[0069] A location call processor 47 is provided for identifying a 911 call
or the like, associating the coordinates information received form the
coordinate estimator 44 with the call, and transmitting the call with the
coordinates information to the interested parties (e.g. the PSAP). As
shown in FIG. 4, this information can be transmitted over the access
network interface as a regular outgoing call, or may be transferred
directly to the PSAP over a separate direct link. Any other suitable
arrangement for transmitting the call with the coordinates information is
possible. It is also to be noted that processor 47 may optionally add
further details to the coordinates information if the UE unit is equipped
for example with a GPS unit. Alternatively, detailed location information
may be compiled at the PSAP; these details are beyond the scope of this
invention.

[0070] Additional embodiments of the invention are network based methods
where the coordinates of the UE unit are determined based on information
inherently provided by the UE unit to the BTS in the uplink subframes.
The uplink subframe 12 (see FIG. 1A) is made up of several uplink bursts
15, 15', 15'' from different users. A portion of the uplink subframe is
set aside for contention-based-access used mainly for a ranging channel
14 which enables the BTS to perform closed-loop frequency, time, and
power adjustments during network entry as well as periodically afterward.
The fundamental mechanism of ranging involves the UE unit transmitting
periodically a randomly selected code division multiple access (CDMA)
code in a specified ranging channel, on a randomly selected ranging slot
in a ranging opportunity defined by the network. Thus, a ranging code is
transmitted by UE unit periodically after it connects to the network and
during various stages of the connection. A number of codes are allocated
to each ranging mode, such as for example an initial ranging, a handover
ranging, a periodic ranging, a bandwidth request ranging (these ranging
modes are so far defined in WiMax Standard). A BTS keeps track of each UE
unit's ranging signal in each ranging mode and then instructs the UE to
adjust its transmission parameters such as timing (advance or retard),
power level, frequency offset, etc or instructs the UE to respond in a
mandate manner (for example, continuously repeat transmitting a BTS known
signal in an allocated radio resource).

[0071] The present invention takes advantage of the ranging signals
inherent to WiMax systems, or any other systems that use a specified
periodic bit sequence (such as periodic ranging, bandwidth request
ranging). Furthermore, according to the invention, a new "location
ranging" signal may be allocated for location identification purposes.
This new location ranging signal may be triggered by pushing a special
purpose button on the UE unit (e.g. a E911 button). To summarize, the
ranging signals are referred generically as an uplink "predetermined
periodic bit sequence", and are very important resources for locating and
tracking a UE unit within a wireless network.

[0072] As seen in the embodiment of FIG. 5, three neighbouring base
transceiver stations BTS-A (the serving BTS), BTS-B and BTS-C receive the
ranging code from the mobile UE unit and perform triangulation using this
signal. As the BTSs are all GPS synchronized, a BTS can estimate the
distance to the UE unit (but not the coordinates) by comparing the time
of arrival of the ranging code provided by its clock, with the time when
the UE unit transmitted the ranging code. This is possible since a BTS
always tracks the ranging codes.

[0073] Similar notations as before are used for the location of the base
stations and the UE unit, namely BTS-A(x1,y1), BTS-B(x2,y2),
BTS-C(x3,y3), and UE(x,y). Each BTS estimates the time of arrival TOA of
the ranging code: BTS-A determines TOA-A, BTS-B determines TOA-B and
BTS-C determines TOA-C. Base stations BTS-A and BTS-B transmit the
estimates to the serving BTS-A, as shown by dotted arrows 5 and 6, and
BTS-A performs the triangulation also knowing the time when, the ranging
code has been transmitted by the UE unit. BTS-A establishes the
coordinates (x,y) of the UE unit as a result of the triangulation.

[0074] Still another embodiment of the invention is shown in FIG. 6. In
this embodiment; the BTS 25 has a distributed antenna system; two receive
antennae are denoted with 20 and 30 on FIG. 6. The coordinates (x1,y1)
and (x2, y2) of these antennae are known and the distance between the
antennae is large relative to the wavelength, but is relative small
compared to the distance between the UE unit and the BTS. The BTS
establishes the equations expressing the circles 40 and 45 by estimating
the TOA of the same ranging code (to the antennae 20 and 30 (the ranging
code is identified based on the time of transmission which is known to
the BTS). Then, the BTS calculates the intersection between two of the
circles, which provides the coordinates (x, y) of the UE unit, as shown
by EQ4:

(x-x1)2+(y-y1)2=r12

(x-x2)2+(y-y2)2=r22 EQ4

[0075] Solving equations EQ4 will give two solutions; the location in
front of the antennae is selected as the result.

[0076]FIG. 7 shows yet another embodiment of the invention that takes
advantage of the multiple antennae systems present at a WIMax BTS. In
this variant, the BTS 25 estimates the angle of arrival AOA of the
ranging code at antenna 20 and estimates the distance to the mobile
(range) to antenna 30. As indicated above, it is known to determine the
distance between the UE and the BTS; however, this location parameter
only enables to establish a circle 50 on which the UE may be located. By
additionally determining a second location parameter (AOA in this
example), BTS 25 can determine the distance `d` to the plane 70 of the
antennae, and then the geographical coordinates (x,y) of the UE unit.
This determination is based on the geographical coordinates of the BTS
and antennae, which are know.

[0077] Once the BIS determines the coordinates of the UE unit, the
information may be automatically appended to the "911" call so that the
operator may determine the exact position of the caller using maps or any
other type of known detailed location information, as discussed above.

[0078]FIG. 8 is a block diagram of the user equipment according to an
embodiment of the invention. This figure illustrates the units relevant
to locating the UE unit based on processing the ranging codes (the
predetermined periodic bit sequence) received in the uplink subframes.

[0079] As in the case of FIG. 4, FIG. 8 illustrates generically the units
of the base transceiver station, namely an interface 81 with the wireless
access network over which the BTS communicates with the UE units, and an
interface 88 between the BTS and a wireless or wireline communication
network. A transceiver 84 shows generically the expected functionality of
the BTS such as, for example for the uplink direction, extracting data
from the frames received from the access network, processing the data,
re-formatting and transmitting it over the communication network towards
destination. Of course, the BTS enables other communication scenarios,
but these are beyond the scope of this invention. FIG. 8 also shows two
receive antennae denoted with Antenna1 and Antenna2 on the wireless
access network (WAN) side.

[0080] In the embodiment of the invention shown in FIG. 8, the BTS
includes a location identifier module 80 including a first monitoring
unit 82 and a second monitoring unit 83. The monitoring units identify
the specified periodic bit sequence (here the ranging code from the
uplink subframe) in the incoming traffic received by the Antenna1 and
Antenna2, respectively. For example, for the embodiment of FIG. 6, the
position parameters determined by the monitoring units are the time of
arrival TOA1 of the ranging code on Antenna1 and the time of arrival TOA2
of the ranging code on Antenna2. Alternatively, the position parameters
are, in the example of FIG. 7, the angle of arrival of the ranging code
on Antenna1 and the distance of the UE unit from Antenna2.

[0081] For the embodiment of FIG. 5, monitoring unit 82 detects the TOA of
the ranging code received at the BTS from the UE unit, and monitoring
unit 83 identifies the TOA measured by two other BTSs and transmitted to
the BTS in a downlink frame (as shown by arrows 5 and 6 on FIG. 5). It is
to be understood that the BTS may be equipped with one monitoring unit
that performs both measurements; this is a matter of design preference.

[0082] In the embodiment of FIG. 5, a position parameters transceiver unit
89 is used to receive and recognize any position parameter transmitted by
the neighbouring BTSs, and to transmit the position parameter measured by
the BTS to the neighbours. Alternatively, the position parameters may be
received and transmitted at a BTS from the neighbours on demand from the
BTS that serves the UE unit for which the location is to be determined.

[0083] The location identifier module 80 also comprises a coordinates
estimator 85 which determines the coordinates of the UE unit based on the
measurements received from the monitors or transceiver 89. For example,
if the coordinates are determined based on the TOA estimates, as in the
embodiment of FIG. 5, the coordinates estimator 85 may perform a
triangulation to obtain (x,y). If the position parameters are the ranges
as in the embodiment of FIG. 6 or a range and an angle of arrival, as in
FIG. 7, the coordinates estimator makes the appropriate calculations as
described above.

[0084] Once the geographical coordinates of the UE unit are determined,
the BTS inserts these in the outgoing 911 call (or the like), as shown by
the location call processor 86, and the call with the location
information is then switched to the destination, shown by location
transmitter 87, where the emergency services or PSAP operators processes
the call accordingly.

[0085] As indicated above, in one embodiment of the invention, the UE unit
is enabled to transmit to the BTS a certain signal, called here a
"location ranging" code/signal that is recognized by the BTS as related
to location determination. This is shown in FIG. 9, where the uplink
subframe provides for a first ranging code 90 and a location ranging code
92. The location ranging code may for example include an identification
of the UE unit and a request for geographical location; this signal is
known to the BTSs. Transmission of the location ranging code may be
initiated by the user or may be automatically triggered at preset
intervals. For example, in a location ranging mode, the UE unit may use
two OFDM symbols where the first OFDM symbol contains a location ranging
code of 144 bits each, while the second OFDM symbol contains the callers
ID and/or requests up to 144 bits.